Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. Which of the following cycles uses air as the refrigerant?

Carnot

Stirling

Ericson

Bell Coleman

2. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Carbon dioxide

Ammonia

Freon

Brine

3. Rating of a domestic refrigerator is of the order of

40 tons

5 tons

0.1 ton

10 tons

4. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

5. The operating pressure for refrigerating units using R-12 as a refrigerant is

2 bar

30 bar

15 bar

8 bar

6. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₁ / (T₂ - T₁)

(T₁ - T₂)/T₁

T₂/ (T₂ - T₁)

(T₂ - T₁)/T₁

7. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

8. Cooling water is required for following equipment in ammonia absorption plant

Condenser, absorber and separator (rectifier)

Evaporator

Condenser

Absorber

9. In a refrigeration system, the expansion device is connected between the

Receiver and evaporator

Compressor and condenser

Evaporator and compressor

Condenser and receiver

10. The minimum temperature to which water can be cooled in a cooling tower is

Ambient air temperature

Dew point temperature of air

Dry bulb temperature of air

Wet bulb temperature of air

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11. The boiling point of ammonia is

-10.5°C

-30°C

-33.3°C

-77.7°C

12. The condition of refrigerant after passing through the condenser in a vapour compression system is

Dry saturated vapour

Superheated vapour

Saturated liquid

Wet vapour

13. In a lithium bromide absorption refrigeration system

Water is used as a refrigerant and lithium bromide as an absorbent

None of these

Lithium bromide is used as a refrigerant and water as an absorbent

Ammonia is used as a refrigerant and lithium bromide as an absorbent

14. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Less

Unpredictable

15. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Negative

Zero

None of these

Positive

16. The domestic refrigerator uses following type of compressor

Axial

Miniature sealed unit

Centrifugal

Piston type reciprocating

17. For obtaining high COP, the pressure range of compressor should be

Low

Any value

High

Optimum

18. The value of C.O.P in vapour compression cycle is usually

Always more than unity

Equal to unity

Any one of the above

Always less than unity

19. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant entropy

Takes place at constant temperature

Involves no change in volume

Takes place at constant pressure

20. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

9: 1

1: 3

1: 9

1: 1

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21. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect liquid refrigerant and prevent it from going to compressor

Collect vapours

Detect liquid in vapour

Superheat the vapour

22. Which of the following is not a desirable property of a refrigerant?

Large latent heat

Good electrical conductor

High risibility with oil

Low boiling point

23. The curved lines on a psychrometric chart indicates

Relative humidity

Dew point temperature

Dry bulb temperature

Wet bulb temperature

24. Which of the following statement is correct?

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(B) The increase in air movement increases the evaporation from the human body.

(D) Both (A) and (B)

25. The freezing point of sulphur dioxide is

-56.6°C

-75.2°C

-135.8°C

-77.7°C

26. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(D) Difference of (A) and (B)

(B) Heat stored in the human body

(A) Heat dissipated to the surroundings

27. The bank of tubes at the back of domestic refrigerator is

Evaporator tubes

Condenser tubes

Refrigerant cooling tubes

Capillary tubes

28. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

1.25

5.12

2.15

29. The vapour compression refrigerator employs the following cycle

Rankine

Reversed Rankine

Carnot

Reversed Carnot

30. The capillary tube, as an expansion device, is used in

Water coolers

Domestic refrigerators

Room air conditioners

All of these

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31. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.67

0.4

0.376

0.6

32. Highest temperature encountered in refrigeration cycle should be

Much below critical temperature

Near critical temperature of refrigerant

At critical Temperature

Above critical temperature

33. In a refrigeration system, heat absorbed in comparison to heat rejected is

Less

More for small capacity and less for high capacity

Same

34. Freon group of refrigerants are

Nontoxic and non-inflammable

Toxic

Inflammable

Non-inflammable and toxic

35. Most thermostatic expansion valves are set for a superheat of

10°C

20°C

5°C

15°C

36. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Super-cooling

Normal cooling

Sub-cooling or under-cooling

None of these

37. A bootstrap air cooling system has

Four heat exchangers

One heat exchanger

Two heat exchangers

Three heat exchangers

38. Critical temperature is the temperature above which

A gas will never liquefy

Water will never evaporate

Water will evaporate

A gas will immediately liquefy

39. A thermostatic expansion valve in a refrigeration system

Is suitable only for constant load systems

None of the above

Maintains different temperatures in evaporator in proportion to load

Ensures the evaporator completely filled with refrigerant of the load

40. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

3.33

2.33

4.33

1.33

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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